flush status;
set query_cache_type=DEMAND;
set global query_cache_size= 1024*768;
drop table if exists t1;
create table t1 (a varchar(100));
insert into t1 values ('aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa'),('bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb');
Activate debug hook and attempt to retrieve the statement from the cache.
set session debug='+d,wait_in_query_cache_insert';
select SQL_CACHE * from t1;;
On a second connection; clear the query cache.
show status like 'Qcache_queries_in_cache';
Variable_name	Value
Qcache_queries_in_cache	1
set global query_cache_size= 0;
Signal the debug hook to release the lock.
select id from information_schema.processlist where state='wait_in_query_cache_insert' into @thread_id;
kill query @thread_id;
Show query cache status.
show status like 'Qcache_queries_in_cache';
Variable_name	Value
Qcache_queries_in_cache	0
set global query_cache_size= 0;
use test;
drop table t1;
SET @old_concurrent_insert= @@GLOBAL.concurrent_insert;
SET @old_query_cache_size= @@GLOBAL.query_cache_size;
DROP TABLE IF EXISTS t1, t2;
CREATE TABLE t1 (a INT);
CREATE TABLE t2 (a INT);
INSERT INTO t1 VALUES (1),(2),(3);
SET GLOBAL concurrent_insert= 1;
SET GLOBAL query_cache_size= 1024*512;
SET GLOBAL query_cache_type= ON;
# Switch to connection con1
SET SESSION debug='+d,wait_after_query_cache_invalidate';
# Send concurrent insert, will wait in the query cache table invalidate
INSERT INTO t1 VALUES (4);
# Switch to connection default
# Wait for concurrent insert to reach the debug point
# Switch to connection con2
# Send SELECT that shouldn't be cached
SELECT * FROM t1;
a
1
2
3
# Switch to connection default
# Notify the concurrent insert to proceed
SELECT ID FROM INFORMATION_SCHEMA.PROCESSLIST
WHERE STATE = 'wait_after_query_cache_invalidate' INTO @thread_id;
KILL QUERY @thread_id;
# Switch to connection con1
# Gather insert result
SHOW STATUS LIKE "Qcache_queries_in_cache";
Variable_name	Value
Qcache_queries_in_cache	0
# Test that it's cacheable
SELECT * FROM t1;
a
1
2
3
4
SHOW STATUS LIKE "Qcache_queries_in_cache";
Variable_name	Value
Qcache_queries_in_cache	1
# Disconnect
# Restore defaults
RESET QUERY CACHE;
DROP TABLE t1,t2;
SET GLOBAL concurrent_insert= DEFAULT;
SET GLOBAL query_cache_size= DEFAULT;
SET GLOBAL query_cache_type= DEFAULT;